Railroads are under increasing pressure to reduce emissions and fuel consumption. In the search for efficient engine and fuel strategies, many different power plant and power delivery strategies have been investigated. Some of these strategies have involved locomotives using multiple engines. For application to locomotives with two or more engines to reduce emissions and fuel consumption, Donnelly et al have disclosed a versatile multiple engine control strategy in U.S. Provisional Application 60/674,837 and a high-power density engine packaging method in U.S. Provisional Application entitled “Multiple Engine Locomotive Configuration” filed Jun. 20, 2005. These applications are also incorporated herein by reference.
Another response in the search for efficient engine and fuel strategies has been the development of hybrid locomotives. Donnelly has disclosed the use of a battery-dominant hybrid locomotive in U.S. Pat. No. 6,308,639 which is incorporated herein by reference. Other strategies to reduce emissions and fuel consumption involve combinations of conventional and hybrid locomotives in a consist
A key component of the strategy to use hybrid locomotives to reduce fuel consumption and emissions is the use of regenerative braking systems which can recover a significant portion of the kinetic energy of a train during braking. Especially in a hybrid locomotive, a successful regenerative braking system requires proper management of a large energy storage system and a specific control strategy for utilizing traction motors as generators during braking.
U.S. Pat. No. 6,615,118 entitled “Hybrid Energy Power Management System and Method” discloses a tender car containing an energy storage apparatus used to capture and store energy that is otherwise not used. The energy storage unit may be charged by the adjacent conventional locomotive when it is not being fully utilized or by a regenerative braking system. The energy stored in the tender car may be used to augment or boost the power supplied by the locomotive to the traction motors on the locomotive or on the tender car itself. U.S. Pat. No. 6,615,118 does not, however, describe specific methods of efficiently recovering regenerative braking energy and managing its transfer to an energy storage system.
U.S. Pat. No. 6,737,822 discloses a power system for an electric motor drive that incorporates a combination of high power density and high energy density batteries to provide a hybrid battery system which prevents electrical recharge energy from being applied to the high energy density battery while capturing regenerative energy in the high power density battery so as to increase an electric vehicle's range for a given amount of stored energy. U.S. Pat. No. 6,737,822 does not, however, describe specific methods of efficiently recovering regenerative braking energy and managing its transfer to an energy storage system.
U.S. Pat. No. 6,441,581 describes an energy management and storage system comprising flywheels and batteries and an energy storage system controller adapted to store energy during load-supplying periods and to supply energy during load-receiving periods. U.S. Pat. No. 6,441,581 does not, however, describe specific methods of efficiently recovering regenerative braking energy and managing its transfer to an energy storage system.
Donnelly et al. have disclosed a method of allocating energy amongst members of a consist in copending U.S. patent application Ser. No. 11/070,848, filed Mar. 1, 2005; and have disclosed a method for monitoring, controlling and/or optimizing the emission profile for a hybrid locomotive or consist of hybrid locomotives in copending U.S. patent application Ser. No. 11/095,036, filed Mar. 28, 2005, all of which are also incorporated herein by reference.
In U.S. Provisional Applications 60/607,194 and 60/618,632, Donnelly et al. have further disclosed a general electrical architecture for locomotives based on plurality of power sources, fuel and drive train combinations. The power sources may be any combination of engines, energy storage and regenerative braking. These provisional applications are also incorporated herein by reference.
Large energy storage battery systems are known, for example, from diesel submarines. Submarine battery packs are designed to provide high energy storage capacity for extended underwater operations during which the battery pack cannot be recharged. Battery pack cost and lifetime are generally not major concerns.
In the late 1990s, a large stationary lead acid battery system was installed at the island village of Metlakatla, Ala. The 1.4 MW-hr, 756 volt battery system was designed to stabilize the island's power grid providing instantaneous power into the grid when demand was high and absorbing excess power from the grid to allow its hydroelectric generating units to operate under steady-state conditions. Because the battery is required to randomly accept and deliver power on demand to the utility grid, it is continuously operated at between 70 and 90% state-of-charge.
It has long been thought that to achieve optimum life and performance from a lead-acid battery, it is necessary to float the battery under rigid voltage conditions to overcome self-discharge reactions while minimizing overcharge and corrosion of the cell's positive grid. This has resulted in batteries being used primarily in a standby mode. As used in hybrid vehicles including hybrid locomotives, however, the battery is rapidly and continuously cycled between discharge and charge over a relatively broad range of total charge.
Systems involving prime movers such as for example internal combustion engines, energy storage systems such as for example battery packs and regenerative braking systems under the control of a computer or controller are well-known. The Prius automobile is such an example. Such a system applied to locomotives is described in U.S. Pat. No. 6,615,118. The latter does not describe how a regenerative braking system can be managed for a hybrid locomotive that includes multiple engines or large energy storage systems connected to propulsion motors by a DC bus nor does it describe how a regenerative braking system can be utilized to optimize battery lifetime in a large battery pack.
There therefore remains a need for specific operating and control strategies to recover energy from regenerative braking, compatible with the use of traction motors and with proper management of large battery pack energy storage systems, so as to provide a system that is economically competitive with or superior to conventional locomotives.